Telescopic actuator

ABSTRACT

A telescopic actuator includes a motor having a rotation shaft, a reduction gear which decelerates an output rotation of the rotation shaft, a feed screw mechanism having a male screw member and a female screw member which are relatively rotated by an output rotation of the reduction gear, a first housing accommodating the motor, and a second housing accommodating the reduction gear and the feed screw mechanism. The first housing and the second housing are detachably attached.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims priority from Japanese Patent ApplicationNo. 2006-352931 filed on Dec. 27, 2006, the entire content of which isincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a telescopic actuator having a motor, areduction gear which decelerates an output rotation of the motor, and afeed screw mechanism in which a male screw member is relatively rotatedwith respect to a female screw member by an output rotation from thereduction gear.

BACKGROUND ART

In a suspension apparatus of a vehicle, for example, an upper link and alower link are controlled to protrude or to retract by an actuator,thereby restraining variations in camber angle and tread of a wheelcaused by bumping and rebounding in order to enhance steering stabilityperformance (see, e.g., JP 6-047388 B2). The actuator includes a motorand a feed screw mechanism in which a male screw member is relativelyrotated with respect to a female screw member by the motor.

The actuator is configured as a single assembly including the motor andthe feed screw mechanism. Thus, when partially changing a specificationof the motor or the feed screw mechanism, it is necessary to redesignthe overall structure the actuator. Accordingly, versatility withrespect to various models is low so that cost is high.

SUMMARY OF THE INVENTION

The present invention is made in view of foregoing circumstances, andprovides a telescopic actuator having enhanced versatility with lowcost.

According to an aspect of the invention, a telescopic actuator includesa motor having a rotation shaft, a reduction gear which decelerates anoutput rotation of the rotation shaft, a feed screw mechanism having amale screw member and a female screw member which are relatively rotatedby an output rotation of the reduction gear, a first housingaccommodating the motor, and a second housing accommodating thereduction gear and the feed screw mechanism. The first housing and thesecond housing are detachably attached.

Other aspects and advantages of the invention will be apparent from thefollowing description, the drawings and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a suspension apparatus for a left rearwheel.

FIG. 2 is a view of the suspension apparatus when seen in a direction 2shown in FIG. 1.

FIG. 3 is a longitudinal section view of a toe control actuator.

FIG. 4 is an enlarged view of the portion 4 shown in FIG. 3.

FIG. 5 is an enlarged view of the portion 5 shown in FIG. 3.

FIG. 6 is an exploded perspective view of a reduction gear and acoupling.

FIG. 7 is an enlarged section view taken along the line 7-7 shown inFIG. 3.

DETAILED DESCRIPTION

Hereinafter, embodiments of the invention will be explained withreference to the drawings. The following exemplary embodiments do notlimit the scope of the invention.

As shown in FIGS. 1 and 2, a double wishbone type rear suspension S foruse in a four wheel steering system vehicle includes a knuckle 11rotatably supporting a rear wheel W (a wheel), an upper arm 12 and alower arm 13 respectively coupling the knuckle 11 to a vehicle body suchthat the knuckle 11 is movable in a vertical direction, a toe controlactuator 14 (a telescopic actuator) coupling the knuckle 11 and thevehicle body to control a toe angle of the rear wheel W, a damper 15with a suspension spring for damping the vertical movement of the rearwheel W.

Each of the upper arm 12 and the lower arms 13 has a base end coupled tothe vehicle body via a rubber bush joint 16, 17 and a leading endcoupled to an upper portion or a lower portion of the knuckle 11 viaball joints 18, 19. The toe control actuator 14 has a base end coupledto the vehicle body via a rubber bush joint 20 and a leading end coupledto a rear portion of the knuckle 11 via another rubber bush joint 21.The damper 15 has an upper end fixed to the vehicle body, e.g., to anupper wall 22 of a suspension tower, and a lower end coupled to theupper portion of the knuckle 11 via a rubber bush joint 23.

When the toe control actuator 14 is extended, the rear portion of theknuckle 11 is pushed outwardly in a vehicle width direction, whereby thetoe angle of the rear wheel W is changed toward a toe-in direction. Whenthe toe control actuator 14 is contracted, the rear portion of theknuckle 11 is pulled inwardly in the vehicle width direction, wherebythe toe angle of the rear wheel W is changed toward a toe-out direction.Accordingly, besides a normal front wheel steering by operating asteering wheel, the toe angle of the rear wheel W is controlled inaccordance with a vehicle speed and a steering angle of the steeringwheel. Thus, straight running stability performance and turningperformance of a vehicle can be enhanced.

Next, a structure of the toe control actuator 14 will be described belowin detail with reference to FIGS. 3 to 7.

As shown in FIGS. 3 and 4, the toe control actuator 14 includes a firsthousing 31 to which the rubber bush joint 20 to be coupled to thevehicle body is integrally provided, and a second housing 32 to whichthe rubber bush joint 21 to be coupled to the knuckle 11 is provided.The second housing 32 supports an output rod 33 such that the output rod33 is protrudable and retractable with respect to the second housing 32.The mutually opposing portions of the first and second housings 31, 32are socket fitted with each other with a seal member 34 interposedtherebetween. The respective opposing portions have joining flanges 31a, 32 a that are fastened together with bolts 35. A brush-equipped motor36, which functions as a drive source, is accommodated inside the firsthousing 31. A planetary gear type reduction gear 37, an elastic coupling38, and a feed screw mechanism 39 having a trapezoidal screw thread areaccommodated inside the second housing 32.

The first housing 31 accommodating the motor 36 and the second housing32 accommodating the reduction gear 37, the coupling 38 and the feedscrew mechanism 39 are respectively assembled beforehand as subassemblies, and the respective sub assemblies are then joined togetheras the toe control actuator 14. The first housing 31 and the secondhousing 32 are joined in a detachable manner. Therefore, the motor 36may be replaced with a motor having a greater output or a smalleroutput, or operation characteristic of the reduction gear 37 and/or thefeed screw mechanism 39 may be changed simply by replacing the subassembly of the first housing 31 or the second housing 31 withoutchanging the entire design of the toe control actuator 14. This canenhance versatility with respect to various models and designs, and thuscan reduce cost.

A yoke 40 having a shape of a cup and a bearing holder 42 constitutes anouter shape of the motor 36. The yoke 40 has a flange 40 a to which thebearing holder 42 is fastened with bolts 41. The bolts 41 are screwedinto the first housing 31 on a surface facing the second housing 32,whereby the motor 36 is fixed to the first housing 31.

An annular stator 43 is supported on an inner peripheral surface of theyoke 40. A rotor 44 is disposed on an inner side the stator 43. Arotation shaft of the rotor has one end rotatably supported on a ballbearing 46 which is provided at a bottom portion of the cup-shaped yoke40, and the other end rotatably supported on another ball bearing 47provided on the bearing holder 42. A brush 49 is supported on an innersurface of the bearing holder 42. The brush slidingly contacts with acommutator 48 provided on an outer periphery of the rotation shaft 45. Aconducting wire 50 extending from the brush 49 is drawn out through agrommet 51 provided on the first housing 31.

The yoke 40, which forms a part of the outer shape of the motor 36, is arigid member for accommodating the stator 43 and rotor 44 therein.Because this yoke 40 is fixed to the first housing 31, a load input fromthe rear wheel W to the toe control actuator 14 is received by the firsthousing 31 so that the load is less likely to be applied to the motor36. Thus, durability and reliability of the motor 36 can be enhanced.Further, a clearance α (a space) is provided between an outer peripheralsurface of the yoke 40 of the motor 36 and an inner peripheral surfaceof the first housing 31. This clearance α restrains an actuation noiseof the motor 36 from leaking out from the first housing 31. Moreover,the clearance α additionally helps to restrain an external force actingon the first housing 31 from being transmitted to the motor 36.

Further, the motor 36 and the first housing 31 are fixed together withthe bolts 41 that are used to fasten the yoke 40 of the motor 36 and thebearing holder 42. Therefore, compared with a case in which the motor 36is fixed to the first housing 31 with bolts other than the bolts 41, thenumber of bolts can be reduced. Also, a space required for arranging theextra bolts can be saved. Accordingly, it is possible to provide the toecontrol actuator 14 of a smaller size.

As shown in FIGS. 3 and 4, the reduction gear 37 includes a firstplanetary gear mechanism 61 and a second planetary gear mechanism 62that are coupled in to have a two-stage structure, i.e., a tandemarrangement. The first planetary gear mechanism 61 includes a ring gear63 fixedly fitted into an opening portion of the second housing 32, afirst sun gear 64 formed directly on a leading end of the rotation shaft45 of the motor 36, a first disk-shaped carrier 65, and four firstpinions 68. Each of the first pinions 68 is rotatably supported on anassociated one of first pinion pins 66 via respective ball bearings 67,and is engaged with both the ring gear 63 and the first sun gear 64. Thefirst pinion pins 66 are press-fitted into the first carrier 65, and aresupported by the first carrier 65 in a cantilevered manner. In the firstplanetary gear mechanism 61, a rotation of the first sun gear 64 (afirst input member) is decelerated and transmitted to the first carrier65 (a first output member).

The second planetary gear mechanism 62 includes the ring gear 63, whichis shared with the first planetary gear mechanism 61, a second sun gear69 fixed to the center of the first carrier 65, a disk-shaped secondcarrier 70, and four second pinions 73. Each of the second pinions 73 isrotatably supported on an associated one of second pinion pins 71 viarespective slide bushes 72, and is engaged with both the ring gear 63and the second sun gear 69. The second pinion pins 71 are press fittedinto the second carrier 70, and are supported by the second carrier 70in a cantilevered manner. In the second planetary gear mechanism 62, arotation of the second sun gear 69 (a second input member) isdecelerated and transmitted to the second carrier 70 (a second outputmember).

As described above, the first and second planetary gear mechanisms 61,62 are coupled together in series. Therefore, a large deceleration ratio(a gear reduction ratio) can be obtained with a smaller size of thereduction gear 37. Also, the sun gear 64 of the first planetary gearmechanism 61 is not fixed to the rotation shaft 45 of the motor 36 butis formed directly on the rotation shaft 45. Thus, compared with astructure in which a first sun gear 64 is provided separately from therotation shaft 45, the number of parts can be reduced. Further, adiameter of the first sun gear 64 can be minimized so that a largedeceleration ratio can be set in the first planetary gear mechanism 61.

The second carrier 70, which is an output member of the reduction gear37, is coupled to an input flange 74, which is an input member of thefeed screw mechanism 39, via the coupling 38. The input flange 74 isformed substantially in a disk shape, and is rotatably supported by apair of thrust bearings 75, 76 holding an outer peripheral portion ofthe input flange 74 therebetween. More specifically, a ring-shaped locknut 78 is fastened into an inner peripheral surface of the secondhousing 32 such that a spacer collar 77 is sandwiched therebetween. Thethrust bearing 75 is arranged so as to support a thrust load between thesecond housing 32 and input flange 74 while the other thrust bearing 76is arranged so as to support a thrust load between the lock nut 78 andinput flange 74.

As shown in FIGS. 4, 6 and 7, the coupling 38 includes two outer elasticbushes 79 made of, e.g., polyacetal, and an inner elastic bush 80 madeof, e.g., silicone rubber. Each of the outer elastic bushes 79 has eightprojections 79 a extending radially from an outer circumference thereof.The projections 79 a are disposed at regular intervals along acircumferential direction of each of the outer elastic bushes 79 witheight grooves 79 b being formed between each of the adjacent projections79 a. Likewise, the inner elastic bush 80 has eight projections 80 aextending radially from an outer circumference thereof. The projections80 a are disposed at regular intervals along a circumferential directionof the inner elastic bush 80 with eight grooves 80 b being formedbetween each of the adjacent projections 80 a. The second carrier 70 hasfour pawls 70 a formed on a surface facing the input flange 74. Thepawls 70 a are disposed at regular intervals, each extending in an axialdirection. Likewise, the input flange 74 has four pawls 74 a form on asurface facing the second carrier 70. The pawls 74 a are disposed atregular intervals, each extending in the axial direction.

The inner elastic bush 80 is sandwiched between the outer elastic bushes79 such that the projections 79 a, 80 a are in phase with each other,i.e., axially aligned. The pawls 70 a of the second carrier 70 and thepawls 74 a of the input flange 74 are alternately engaged with eightgroove sections, each of the sections being formed by the grooves 79 b,80 b that are axially aligned.

Accordingly, a torque of the second carrier 70 is transmitted from thepawls 70 a of the second carrier 70 to the input flange 74 through theprojections 79 a, 80 a of the outer and inner elastic bushes 79, 80 andthe pawls 74 a of the input flange 74. The outer elastic bushes 79 andthe inner elastic bush 80 are both made of elastic material. Thus, theouter elastic bushes 79 and the inner elastic bush 80 absorb a slightaxial difference between the second carrier 70 and the input flange 74,and also absorb a sudden change of the torque, thereby enabling a smoothpower transmission.

As shown in FIG. 5, a first slide bearing 91 is fixed to the inner 2Cperipheral surface of the second housing 32 at an intermediate portionof the second housing 32 in the axial direction. A second slide bearing92 is fixed to an inner peripheral surface of an end member 93 screwedonto an end portion of the second housing 32 in the axial direction. Theoutput rod 33 is slidably supported by the first and second slidebearings 91, 92. The feed screw mechanism 39 converts the rotation ofthe input flange 74 to a thrust movement of the output rod 33. The feedscrew mechanism 39 includes a male screw member 95 penetrating throughthe center of the input flange 74 and fastened with a nut 94 (see FIG.4), and a female screw member 96 threadedly engaged with an outerperipheral surface of the male screw member 95. The female screw member96 is fitted inside the inner peripheral surface of the hollow outputrod 33, and is fixed thereto by a lock nut 97.

As described above, the output rod 33 is supported inside the secondhousing 32 a plurality of slide bearings 91, 92 (two in the embodiment).Therefore, a radial load applied to the output rod 33 can be reliablysupported by the second housing 32, thereby restraining the radial loadfrom being applied from the female screw member 96 to the male screwmember 95.

A spring base 99 is supported via a thrust bearing 98 at a leading endof the male screw member 95. A coil spring 101 is compressed between thespring base 99 and another spring base 100 provided on a leading end ofthe output rod 33. The spring force of the coil spring 101 biases thefemale spring member 96 fixed to the output rod 33 and the male screwmember 95 in threaded engagement with the female screw member 96 inopposite directions respectively, thereby eliminating play betweenthreads of the male and female screw members 95, 96.

According to the above configuration, the threads of the male and femalescrew members 95, 96 are always in close contact with each other so thatfrictional force is generated. Therefore, in a case where a vibratoryload is input to the female screw member 96 from the rear wheel W, orwhere a large load is input to the female screw member 96 from the rearwheel W, it is possible to prevent the male screw member 95 fromrotating spontaneously and thus to prevent the toe angle of the rearwheel W from changing unexpectedly. Thus, control accuracy of the toeangle is improved. As a result, there is no need to apply a current tothe motor 36 for the purpose of restraining an unintentional rotation ofthe male screw member 95, reducing power consumption of the motor 36.

A stroke sensor 102 is provided in the second housing 32. Whencontrolling a telescopic movement of the toe control actuator 14, thestroke sensor 102 detects an axial position of the output rod 33 andfeeds back the detected axial position to a control unit. The strokesensor 102 includes a detectable portion 104 fixed to the outerperipheral surface of the output rod 33 with a bolt 103, and a sensormain body 106 accommodating a detecting portion 105 which detects aposition of the detectable portion 104. The detectable portion 104 maybe a permanent magnet, and the detecting portion 105 may be a coil whichmagnetically detects the position of the detectable portion 104. Thesecond housing 32 includes an opening portion 32 b which provides aclearance having a certain length in the axial direction. The openingportion 32 b allows the output rod 33 and the detectable portion 104 tomove without interfering with the second housing 32.

A ring-shaped stopper 107 is provided on the outer periphery surface ofthe output rod 33. When the output rod 33 is moved in a protrudingdirection, the stopper 107 eventually hits a contact surface 93 b of theend member 93, whereby the output rod 33 reaches its outermost position.Thus, even when the motor 36 rotates out of control due to some kind offailure, the stopper 107 reliably prevents the output rod 33 fromslipping out of the second housing 32. Because the stopper 107 isdisposed within a dead space between the first and second slide bearings91, 92, a space can be saved. The end member 93, on which the secondslide bearing 92 is provided, can be separated from the second housing32. Therefore, the output rod 33 equipped with the stopper 107 can beattached to and detached from the second housing 32 without interferingwith the second slide bearing 92.

A boot 108 is provided in order to prevent water and dust from enteringa gap between the second housing 32 and output rod 33. The boot 108 hasone end portion fitted in a circumferential stepped portion 32 c of thesecond housing 32 and the other end portion fitted in a circumferentialgroove 33 a of the output rod 33. The respective end portions of theboot 108 are then fixed by associated bands 109, 110. A flange 93 a ofthe end member 93 forms a circumferential groove together with thecircumferential stepped portion 32 c of the second housing 32. Thus, theend portion of the boot 108 fixed by the band 109 can be prevented fromslipping off. Because the flange 93 a of the end member 93 is utilizedto prevent the boot 108 from slipping off, it is not necessary to form acircumferential groove on the second housing 32. Compared with a processof forming a circumferential groove on the second housing 32, a processof forming the circumferential stepped portion 32 c is easier. Further,because the circumferential stepped portion 32 c requires only oneshoulder portion while a circumferential groove requires two shoulderportions, a dimension of the second housing 32 in the axial directioncan be reduced by an amount equivalent to a width of one of the twoshoulder portions.

When the output rod 33 telescopically moves, inner pressure the firstand second housings 31, 32 changes, and this might obstruct a smoothactuation of the toe control actuator 14. Thus, a hole 33 b is formedthrough the output rod 33 so as to communicate an internal space of thehollow output rod 33 and an internal space of the boot 108. This hole 33b allows the boot 108 to absorb the change of the above-mentioned innerpressure by deforming, thereby enabling the smooth actuation of the toecontrol actuator 14.

Although a telescopic actuator according to the present invention isused as the toe control actuator 14 in the above-described embodiment,it may be used for other various purposes. When a telescopic actuatoraccording to the present invention is used as the toe control actuator14, a load to be downwardly applied to the spring of the suspension Scan be reduced due to its small size and light weight.

Also, although the feed screw mechanism 39 has the trapezoidal screwthread in the above-described embodiment, other types of screws may alsobe used, e.g., a ball screw.

While description has been made in connection with embodiments of thepresent invention, those skilled in the art will understand that variouschanges and modification may be made therein without departing from thepresent invention. It is aimed, therefore, to cover in the appendedclaims all such changes and modifications falling within the true spiritand scope of the present invention.

1. A telescopic actuator comprising: a motor comprising a rotationshaft, a yoke, and a bearing holder supporting the rotation shaft, theyoke and the bearing holder forming an outer shape of the motor; areduction gear which engages with the rotation shaft to decelerate anoutput rotation of the rotation shaft; a feed screw mechanism comprisinga male screw member and a female screw member which are relativelyrotated by an output rotation of the reduction gear; a first housingaccommodating the motor to form a first sub-assembly such that an innerperipheral surface of the first housing surrounds an entire outerperipheral surface of the yoke; a second housing accommodating thereduction gear and the feed screw mechanism to form a secondsub-assembly, being detachably attached to the first housing, and a boltpenetrating the bearing holder and the yoke to fasten the bearing holderand the yoke to the first housing, wherein the first sub-assembly andthe second sub-assembly are detachably attached together such that, whenthe first housing and the second housing are detached from each other,the rotation shaft of the motor and the reduction gear are disengagedfrom each other while keeping the bearing holder and the yoke fastenedto the first housing.
 2. The telescopic actuator according to claim 1,wherein a space is provided between the outer peripheral surface of theyoke and the inner peripheral surface of the first housing.
 3. Thetelescopic actuator according to claim 1, wherein the first housingcomprises a first flange outwardly extending in an radial direction ofthe rotation shaft, the second housing comprises a second flangeoutwardly extending in the radial direction of the rotation shaft, andthe first flange and the second flange are fastened together to attachedthe first housing and the second housing.
 4. The telescopic actuatoraccording to claim 1, further comprising a conducting wire through whichelectric power is supplied to the motor, wherein the first housing isformed with a hole through which the conducting wire is led outside thefirst housing, the conducting wire being spaced away from the secondhousing.
 5. The telescopic actuator according to claim 1, wherein thereduction gear is fixedly fitted inside the second housing.
 6. Thetelescopic actuator according claim 1, wherein a part of either one ofthe first housing and the second housing is fitted inside the other ofthe first housing and the second housing.
 7. The telescopic actuatoraccording to claim 1, wherein the yoke comprises a flange facing thebearing holder, wherein the bolt penetrates the bearing holder and theflange of the yoke in an axial direction of the rotation shaft.
 8. Avehicle suspension comprising: a knuckle adapted to rotatably support avehicle wheel; a damper coupled to the knuckle; and the telescopicactuator according to claim 1, wherein the telescopic actuator iscoupled to the knuckle, and is operable to change a toe angle of thevehicle wheel.
 9. The telescopic actuator according claim 1, wherein thebolt is screwed into the inner peripheral surface of the first housingsuch that the bearing holder and the yoke is fastened between the boltand the inner peripheral surface of the first housing.
 10. Thetelescopic actuator according claim 1, wherein the bearing holder is aseparate component from the first housing.
 11. The telescopic actuatoraccording claim 1, wherein the reduction gear is provided between therotation shaft of the motor and the feed screw mechanism such that theentire feed screw mechanism is contained in the second housing.
 12. Thetelescopic actuator according claim 1, wherein the feed screw mechanismcomprises a radially extending input flange having a substantially diskshape, and the reduction gear comprises an output member coupled to theinput flange.
 13. The telescopic actuator according claim 1, furthercomprising: an end member connected to an end portion of the secondhousing; an output member housing in the second housing and extending atleast partially through the end member; and a stopper provided on an endportion of the output member, such that when the output member is movedaxially within the second housing in a protruding direction, the stoppercontacts the end member to prevent the output member from disengagingfrom the second housing.
 14. The telescopic actuator according claim 1,wherein the reduction gear includes a first planetary gear mechanism anda second planetary gear mechanism, the first and second gear mechanismbeing coupled together in series and being entirely housed in the secondhousing, the first gear mechanism being operably connected with themotor rotation shaft, the second gear mechanism being operably connectedto the feed screw mechanism.